Fiber optic interferometric sensors are known in the art and have been used to detect environmental effects, such as strain, temperature, acceleration, acoustic signals, and vibrations. In one type of sensor based on a Sagnac interferometer, also known as an optical fiber ring interference sensor, an optical wave is split and directed in clockwise and counterclockwise directions around an optical fiber loop. The waves interfere at an optical coupling element after passing through the loop. A phase difference between the two waves is caused when the optical fiber loop is exposed to an environmental effect, and the intensity of the combined wave is based on the relative phase of each of the clockwise and counterclockwise optical waves. The sensor then employs a signal processor to analyze the intensity variations and determine information about the environmental effect. Additional information regarding optical fiber ring interference sensor configurations is provided in U.S. Pat. No. 6,798,524 to Takashima et al., the entire disclosure of which is incorporated by reference herein in its entirety for all purposes.
It is also known to measure amplitude and position of vibrations using a distributed sensor comprising a combination of wavelength division multiplexed Sagnac interferometers operating on different wavelengths. Such a sensor is disclosed in U.S. Pat. No. 5,402,231 to Udd, which is incorporated by reference herein in its entirety for all purposes.